1. Field of the Invention
The present invention relates to a substrate for epitaxy and an epitaxy using the substrate and more particularly to a semiconductor substrate wafer for epitaxy and an epitaxy of a compound semiconductor layer on the compound semiconductor substrate wafer by the metal organic chemical vapor deposition (MOCVD).
2. Description of the Related Art
Conventionally, an epitaxy of a layer of a compound semiconductor single crystal on a substrate wafer of a compound semiconductor single crystal causes the epitaxial layer to experience surface defects (referred to as teardrop-like hillock defect hereinafter) such as ellipsoidal micro protuberances that are arranged in a certain direction across the surface of the layer.
In order to eliminate the defects described above, the present inventors filed a patent application in Japan (see the Japanese unexamined patent application publication HEI.2-239188). This patent publication discloses an epitaxy under conditions that a compound semiconductor substrate wafer for MOCVD epitaxy of which the orientation of the surface is deviated 0.1.degree.-0.5.degree. from the &lt;100&gt; plane is employed and that the temperature of the substrate wafer is 600.degree.-700.degree. C.
The epitaxy disclosed in the Japanese patent publication has an advantage of remarkably reducing the number of teardrop-like hillock defects. After the filing of the Japanese patent application, the present inventors reviewed the epitaxy disclosed in the Japanese patent publication and found another problem. While the epitaxy advantageously reduces the number of teardrop-like defects, an excess of the orientation off-angle of the substrate wafer surface from the &lt;100&gt; plane causes wrinkled defects on the epitaxial layer grown on the substrate wafer surface. The present inventors also found out that an epitaxy using a substrate wafer of which the surface orientation off angle from the &lt;100&gt; plane is lower than 0.1.degree. may provide no teardrop-like hillock defects to the surface of the epitaxial layer grown on the substrate wafer. The present invention was made on the above background.